In what ways is the word “work” as used in everyday language the same asy*.eu0aq fhuqk( s 4*v that defined in physics? q. * eksf uu4yq(hav*0In what ways is it different? Give examples of both.

Can a centripetal force ever do of 63- dmontd9work on an object? Explain.

Can the normal force on ah pf6(gif qzw98 r1-obx7u2ua n object ever do work? Explain.

A woman swimming upstream is not moving with respect to ju k6p y-/4hvg6afg/r1rd u5lthe shore. Is she doing any work? If she stops swimming and merely floa4hv uy6 dg6 r/alg/1-u 5pfrkjts, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider twd t 5p(s dly,un)+r:what happens to the dishes when you pull a tableclothuln(+ ys,wdtdt p)5:r out from under them.]

Why is it tiring to push har6 ,u9wb9fsv-v:ajym - umeor;.d7 lqv d against a solid wall even though you are doing no workvdsbv-7:6voy; lre .9jfmqm -w , ua9u?

You have two springs ,,jsca7: yn:nc9is rxzdf8 .8xwjh4 nthat are identical except that spring l is stiffer than springnwcr x: 7ac8j.j,fs,9 n xd8:i hy4zsn 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that w2 x4-l+u 5wwzdf1 dbkis free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled d+4fdxulw5zwwkb1 -2 a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational pzxf;5(8y a-uyxlqw(hr :4z ) sy2tuhhotential energy change when you jump as high as you can?uh(8w:yh ty x2-4;y)qrual(sz5f zh x

In Fig. 6–31, water balf x;/ puxdu-d-loons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignor/; pdxux-df -ue air resistance.

A pendulum is launched from a point that is a height i92n7 d4vxaaisbc p-zzb0d. +h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along 2zz4+v iba97xsba- incpd0d.the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring b2t zn9bh o9c8ay pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conserv8 tzoabc9hn 92ation of energy.

A bowling ball is hung from the cv*c:xzl n6 sh/eiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. Tolz6vhs/cx: * n avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational d d4- blv)0g fm.azcq9nz j04.kmlqh:potential energy when water at the top of a waterfall falls to nak0).zlq fch:4 m-vjl0d z. 9 bdq4gmthe pool below?

Describe the energy transformations when a child hops around on a p37/5n*j *2eyrbm-h0y f fhcem;bxz 1ag* oslpogo stick.

Describe the energy transformations that take place when a skier starts ski(q+zrw mjio4qm6kt 0dml;8uqc nn :: .ing down a hill, but after a time is brought to rest b m:nqwl ntd:4 86+k0cq juiqzm;.mro(y striking a snowdrift.

A child on a sled (total mass m) starts from rest a h:.hri9jy yctc4 2z-bt the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no t4-.:2hri c zyb9yjhcfriction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step oy(t+1r x;upuwe9 vjnctg9f 61 ver a fallen log in their path rather than stepping on top and jumpi+t gf9 61vt; 1uwn9rc yejxup(ng down on the other side. Explain.

Two identical arrows, one with twice th dtbrr/+z /eq2e speed of the other, are fired into a bale of hay. Assuming the haybr 2rqez/ d+t/ exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a siy24xj 8pxdt3 ample swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account.xdj4y ax2 t3p8 Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height5s,i2/ils2mvv zp;ardyx- l- greater than its original height? Explax/z52sa -,i-vpiyr; lds2l mvin.

Suppose you lift a suitcase from the floor to a table.) -x( k1ickz(oz;ftfd f 1;jgw The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a11kfx- k;co(z)wdzgtff(i j; more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power jf8 (9c2pm gxmneeded rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to cl8wzk x:du3 a:iwr3 e9+irh 3rbimb straight upe wak3+8zd wb irui3h:r:xr39?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes n4;mbzg*4pku .43uk9sl0hax wu f0d uto decrease the force needed to raise a heavy load (see Fig. 6–34). Bud .4hs03fnauuu mgk uw z *;40p4lk9xbt for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a h4 n*fb2dcry -265-kg pile driver falls yf -r2d*4nc bh2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m hig-m/v2/cj1ddbz 9 naj0 s1alkf h. How much work is requiredmd d9/zab f/njj vls12 k-ca10?    J

  A 1300-N crate rests on the floor. How much work is required to move it at cql,x:cb7sf nmg5p,s1 onstant speed (a) 4.0 m along the floor against a friction force of 230c sf1spl b7m,n,x:qg5 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontalot3okb;/xn16w n 5xvz ly) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the;w/voxno5 x1k 3tbzn 6 effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of fordp9/ 4/ou5uhq 1hlayl 7.0 s. Find the net work done on the ba /lp9h 5hqlouu 1d4/yox.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, l/brymm5b-2 -it4a k* h:f, hv leopjl,ie flat on a table. How much work is required th *b- / lve - yhl5martk:,pofj4b,m2io stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mighti) c vupk7/q7s not otherwise be able to liff. Show that thec/sp7v7 ukiq ) ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and rzueocmk.)4ca 78-s yd4qo/r is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficientucor ezs)k4c 8d -mqa.ro /47y of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force requiretus 1y2u3m1ev)ay6e(cq+a xy d to give a helicopter of mass M an acceleration of 0.102 )y+1y1ecevusx( 36uq atmay g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distanb- epxs4d)c1rq+,wswctiw -,ce axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axj6 3rrubu -az)is, varies as shown in Fig. 6–37. Determine the w)r3z - 6aujbruork done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle 4( vtc5*a tztxqs8u m:acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mro*nk*1hs i mvj*ar + bs*xa5,ass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has itfoh1f kv*soohmh( e,;9pyi)4k bv)(ts speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elri dmug6 )*zz4ectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to st1z+u/co, zet 3uw+ngu op a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a hqkv2s;s h)hc1 d:7p ;et;rhabow whose string exerts an average force of 110 N on the arrow over a di1hv;d;p)s7kshqr:ah; hc t e2 stance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 3+p ((sqxdpgq5 2m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the a (p5qpxs(dqg +verage force exerted by the ball on the glove?    N

If the speed of a car is increash:z+xziu w- e *s,qy)ied by 50%, by what factor will its minimum braking distance be increased, ass*: h zzu xi-)iq,yesw+uming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level roadmqfok:y1h ibrjff7f,6x ), 8 z, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of q71yhkjfm i:,fbo)f xz68,rf the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time itpq y9f zyfq;xj;0j48k3*g6crl *deg i reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average 39kye f 4qd**gj yi lz8cfxqrjg06p; ;force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone whoxwj +yqd (j-s8 does 80.0 J of work on it? Neglect air resistance(jw- q8jyx+sd.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratio5jruxc. 8cbtyhl3 d(1n by a single cable. Dete1yxb 3c . (j5culdr8thrmine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k,ag)svgql4mi7ac mj mb f;* dk7 n/f2+: of 440N/m How much must this spring be/s*gm av:ffkq l7;gcji m)n7am+d 24b stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the /f/ w-ja-3k9fmeqpr gchange in potent /-mqf kj/eg r3pwa-9fial energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaultva37 qs9xe7bpls dggd-m0;gxa7h . (xer change if his center of mass rises about (p 97; be xg3gdg 0l7aqmh7vsaxs.dx-4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v xb/f fsf* ;.py= 65 km/h when it strike;sfpy f.x* /fbs a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so itsqpf wc,uu4q 5:s9t-g 4mm3xb is 2.20 m above the ground. What is the potenti4xwt93cqsf5us 4m: bpmq gu -,al energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at de- zuyie9 4q-an elevation of 1600 m and climbs to the top of a 3300-m peakiyeqd ue-9 4-z.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The eg s ijmgc3ga)p wvxa08a4t- ;2nd of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the w8a ;-gmap 3agtvs2igc j)4x0spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top sp:0k;okjem3cd)a l2t meed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing3 : lmokmek)j2at; dc0 upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slid+)uwu5cg yl 7k.bv.1j*:c- n kaeqjtkes down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove: ix3haxfzb259 kz ,yez4u,l a up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational poten +t;ihq-zeqenh7v lk9o5;;k itial energy without the aid of a inth o7v5kqh keel -i+z;9;q ;pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verp:81 t zy dy;il:scw:wtically upward from the top of a platform wit 1lyt :pw:dy8w izcs;:h a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignorezfjb2 ud2 avz:ke+/xxqa)m+ ) its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it givjvqz e a2x+abd: xfk m))+zu2/e to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped tr -ntzn55x.j xcack shown in Fig. 6–39. If the block is tcz tjx.55n-nxo remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffnw tgr)zw,o0xy8ul ;)s ess constant k),8w)u)s ot w; gxylz0r, Fig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bud qwag8*czv .q8(y zv(ngee cord whose unstretched length is 12 m, and falls a totqz8gz( 8.qvyw ( dac*val of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41o5lwkhv *+e4 w is dragged up to point 1 where it is rk*4w+w h vl5eoeleased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an av d2dcent9j wp08 7yn-ngle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an elevo /nigot3 )2xqator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass qo23/) txg ionof the elevator and passengers.

  A cyclist intends to cyc xkol2*sbto6 8le up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite dig uh2a+n:qp +j3fkhk( rections, collide head-on and come to rest. How mu gkqk 2a+hph3(fun:+ jch thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottomgm:d9/i3 (ac+bntefx with a speed of 9 c/+a: ngfmidbx( 3et2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slapnb,o9hffn i9,93k a ides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the grzgw q*s,;w4:h uf)ib gk(dc 4pound.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a heigws ;q v)ev,fp(b80s; zilvpe1ht of 1.5 m80 v1 episqlb(v e;z;,pwvf) s.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulgm.)6 p6noxh qym mh6-led across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and f)p6xqogmy.h 6mm6-n hor the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in l rysjay1b* tk1gp,.:8aw*a lFig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed 8*lk jlsr: w yyb,apa *.a1gt1will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a 4ycn10 dy 6+jk 7urzkeqh,u va2m;p/bsteady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (k=18u8wg:( h)7uqg htggrn-x 6jvrzj k:090N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between ttk( ru8 -hx v6 rjh)gg 0:9uz:ng7wjqghe block and the table?   

  A 280-g wood block is f,c(v 1 62lkm(cvowc hyirmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of f(hv2,ko v c6ycm(c1wl riction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights f1wy j 3c+lp6uw al5u3vor the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at +1pj5uuy6lwvc3l wa 3a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor t9;cl s.c z ;8u3v s2i. sqcjrnbhg0i:ro lift a 315-kg piano to a sixth-story window 16.0cvjqs.r :hn;u9i ;30bz r c2slsi.cg8 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must betd* f5c iu43wg the average force exerted on the car due to friction and air w u4c3fgid5* tresistance?    N

  A 1400-kg sports car accelerates from resuzar b* 3vlr m.pf84deu17z9 lt to 95km/h in 7.4 s. What is the average power delivered by the ev .*9e1rlu 8r4m b37pf luadzzngine?$\approx$    hp

  (a) Show that one Briydc h e6xu2f n4p.)t5ety08bte4g ,aztish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy unit)qp)n3z6 tvku ozu/gn)gm33 bs are often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kwfis7-j+ kjk (g car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep th fswkki(j-+7je car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mot 7:p9 pa.7wr 3mcy t6zqwtok nb;oci59or do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If ti+ (zv;b9-w2sv ) 0qkkdxak:bcdiu v2his motion takes 1.5 s, what aver 9vik(z vd0vd-2qi ;bw 2a:)kscub xk+age power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per miza2np;c *e njejy2iw8*)-b avnute through a height of 3.60 m. What output rating (watts) should the pump motor 8-byavicwj 2)nnza;2* eej* phave?    W

  During a workout, the e53n +jowbb d,football players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined atdojbw35e+b ,n an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cycla a*ka8hb *,mrist climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hf-va l2rwzzap0tpwv+6tl7h ev2+ -y5p. How steep a hill can it climb at a constanthw a052v-w7va+y6-p+ttfzlz 2rplv e speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have k0 6n;jax1i2p- sozsd to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient10szxj 6d2oia- s;npk of friction is 0.45?    hp

  A bicyclist coasts dow pba4jms9);cun a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bw (k hy --psaom/l*-h;akk 1wfumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after aa- -1wyphks hlk m*oa /fk;w(- compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remad;cm ,ddhwx;71zcz5j.e /owd ining four shelves are each spaced 30/cm;ddoz dj c 1w.7 ,w5;hdxze.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in tdqj9p7f9g h 7lv0kq , b6h a8qpc6fz9rhe 1936 Olympics shows thatjgh 99 z a9l6vd6pkqq0fc7 8p,r7hb fq his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the lot u6s to ook;sw2gd7rx8;mr5 )oped track shown in Fig. 6–39 is to remain on the track at all times, evtmtgs5)o r8 s 7ou6rxkw;o2 d;en at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hi hsdm n-1au//grhh *3us parachute opmuhadr-h nh 3//1su*gening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L w vj8pp7o,nms 9hose other end is fixed (Fig. v97pj, pon ms86–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to th)i(qq tpgxebf /uf+ (/e top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 230/pq bg(iqtu)ffex (/+0 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m pm)*j zd;2q hiabove a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in Ce : no08 er9x3y awy,lx/vr,qhalifornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power near0vehlw,, e q x8/3: yxnor9yeded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically*7vzd c0 )xt8w77moq v ybobv5du -pk2 81 m before striking the turbine blades. Calculated v- *7xy50 2uzobd q7mot wp7bk)8vcv
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a o zg: +)gpni fxrzklp;tl,. t,2w;g -ucircular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the l.+iztok)glgn g;:p ,,- uw l;rftx2pzoop or how fast you go through it.    mg

  (a) If the human body could coi0e s-it5qn*f(uu1gz.exsq4 nvert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled fqug0ste5 sni e xi14z(.*u-qby one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward anglegmon x6 *u8s.j of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresscckj)z gijbo.*( ;g eg.tnn//es 0.60 mm, and it tells you your weight is 710 .oi )n*b/j cgg g/j(;ke.n cztN. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs )q q1uhk21 0hkycju15/zerniat 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope whenq)zuu1heic hy q 05k/ jkn21r1 his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 7 4k7/;w myodmm-byzh(3 ql7uy 2-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this fe7/3k4-zlmbmyuohw m; (7yydq at?    W

  Some electric-power companies use water)uj694jyy b7iw b.r fe to store energy. Water is pumped by reversible turbine pumps from a low to a hibw6).ij7 uj9fby4yr egh reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What s26 7.yja(4zynzn gbc is the spring stiffness constant for each of the two resulting springsn y(7cynsa 2gz. 4jzb6?   k

  A 6.0-kg block is pushed 8.0 m up a rougm-53 -e leml5fos4lds h 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h tohnnzqq61 7ymyp4r5gfe-1b3 t 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictiona6e -417y nptqbz15y mghfn3rql losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks v 4k izc29chg*on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75*g ic4hv29 czk-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock verticalky8n43mw we g9.f9ljmtk 8y1yt l:0jy ly upward a distance of 500 m, what was its velocity when it left the volcano? 8 :98wy ktgj0 3l1y 94fetkyy.mwjnl m $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0kk4evmb31a1y fo1 i 0l m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, wmk 1blyv31k4e faoi1 0hat is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s